1. Field of the Invention
The present invention relates to an ocular refractive-power measuring device for calculating the refractive power of an eye to be examined by projecting light rays for measuring ocular refractive power toward the fundus of the eye to be examined and by analyzing the state of the reflected light.
2. Description of the Related Art
In an ocular refractive-power measuring device, the refractive power of an eye is measured by projecting the light rays of a pattern for measuring ocular refractive power through the pupil of an eye to be examined, and by receiving the light reflected from the fundus. Accordingly, if the optical axis of measurement and the center of the pupil are substantially offset from each other, the light rays of the pattern for measurement is eclipsed by the pupil, and a measurement error occurs. Hence, it is necessary to align the optical axis of measurement with the pupil at the time of measurement.
Meanwhile, an ophthalmologic apparatus, such as the ocular refractive-power measuring device and a non-contact type tonometer, is provided with an alignment detecting mechanism for optically detecting the position of the eye to be examined. As the detecting method, there have been proposed a method in which the optical axis of measurement is aligned with the corneal vertex by using the corneal reflecting light rays and a method in which the optical axis of measurement is aligned with the central position of the pupil by detecting an edge of the pupil on the basis of an image of the interior chamber.
In most eyes to be examined, the corneal vertex and the corneal center are generally aligned with each other, but there are not a few eyes to be examined in which the corneal vertex and the corneal center are offset from each other in cases where orthokeratologic operations or the like have been performed. For this reason, if the method of aligning the optical axis of measurement with the corneal vertex by using the corneal reflecting light rays is adopted in the ocular refractive-power measuring device, even if the completion of alignment is detected, there can be cases in which the pupil is actually eccentric with the optical axis of measurement. Consequently, the light rays of the chart for measuring ocular refractive power is eclipsed by the pupil, resulting in a measurement error.
To solve this problem, in Japanese Patent Unexamined Publication No. Hei.11-19040, alignment detection is effected by the corneal reflecting light rays, and the position of the pupil is also detected after detection of the completion of alignment. If it is determined that the pupil is offset, an automatic alignment mechanism is driven (if the automatic alignment is not adopted, an alignment inducing mark is displayed on a monitor so as to prompt an examiner to effect manual alignment) so as to align the optical axis of measurement with the pupil, thereby preventing an increase in the measurement error or the occurrence of the measurement error itself.
With Japanese Patent Unexamined Publication No. Hei.11-19040, however, a control mechanism for effecting automatic alignment based on a pupillary image is present in conjunction with a control mechanism for effecting automatic alignment based on the corneal reflecting light, and after detection of the alignment based on the corneal reflecting light, the position of the pupil is detected and whether or not the pupil is within a predetermined range is detected. If this method is adopted, after completion of the automatic alignment based on the corneal reflecting light, an additional time period longer than {fraction (1/30)} second is further required for detection of the position of the pupil. In the meantime, despite the fact that the alignment with the corneal vertex has been successfully completed, there is a possibility of the eye to be examined becoming positionally offset again due to involuntary eye movement or the like, thereby making it difficult to complete the alignment.
Accordingly, an object of the invention is to provide an ocular refractive-power measuring device which has a mechanism for alignment with the corneal vertex for facilitating the detection of a signal, and which is capable of reducing an error in the measurement of the ocular refractive power as much as possible.
To attain the above object, there is provided an ocular refractive-power measuring device for measuring the refractive power of an eye to be examined, comprising: a refractive power measuring unit projecting pattern light rays for refractive power measurement onto a fundus of the eye to be examined, receiving the reflected light of the pattern light rays from the fundus by a light receiving element and measuring the refractive power of the eye to be examined on the basis of a shape of the pattern light rays projected onto said light receiving element; an alignment detecting unit projecting light rays for alignment detection toward the eye to be examined and detecting a state of alignment between a vertex of a cornea of the eye to be examined and a device body on the basis of corneal reflecting light of the light rays for alignment detection; an alignment unit aligning the device body on the basis of an output of the alignment detecting unit; a storage unit storing the shape of the pattern light rays received by the light receiving element; and an eclipse detecting unit detecting the presence of an eclipse in the pattern light rays due to a pupil of the eye to be examined on the basis of the shape of the pattern light rays stored in the storage unit, and a direction of the eclipse, wherein, when the eclipse detecting unit detects that the eclipse is present, the alignment unit adjust moves a position of the device body on the basis of a result of detection by the eclipse detecting unit such as to adjust an alignment between the pupil of the eye to be examined and the device body.
In accordance with the ocular refractive-power measuring device, alignment with a corneal vertex is effected by the alignment unit, and the pattern light rays for ocular refractive power measurement is projected toward the fundus of the eye to be examined. The pattern light rays reflected from the fundus is received by the light receiving element, and the refractive power of the eye to be examined is measured on the basis of the shape of the pattern light rays.
The pattern light rays received by the light receiving element is stored by the storage unit, and the eclipse direction detecting system detects the presence or absence of an eclipse in the pattern light rays due to the pupil of the eye to be examined on the basis of the shape of the pattern light rays stored in the storage unit, and detects the direction of the eclipse if the eclipse is present.
If it is determined by the eclipse direction detecting system that an eclipse is present, adjustment of alignment between the pupil of the eye to be examined and the device body is effected by adjustably moving the position of the device body on the basis of the result of detection by the eclipse direction detecting system.
In a case where a positional offset is present between the corneal center and the pupillary center, adjustment of alignment between the pupil of the eye to be examined and the device body can be effected on the basis of the result of detection by the eclipse direction detecting system. Therefore, the eclipse of the pattern light rays by the pupil can be eliminated, so that an error in the measurement of refractive power can be reduced.
In addition, in a case where there is no positional offset between the corneal center and the pupillary center, the refractive power can be measured on the basis of the pattern light rays stored by the storage unit, so that the possibility of the eye to be examined becoming positionally offset due to involuntary eye movement or the like can be reduced.
In addition, the alignment adjustment based on the result of detection by the eclipse direction detecting system may be effected manually. However, if movement controlling unit is provided for controlling the movement of the position of the device body on the basis of the result of detection by the eclipse direction detecting system, it is possible to effect the alignment adjustment by automatic control. In this case, as a mechanism for driving the position of the device body, a driving mechanism for effecting the adjustment of alignment with the corneal vertex can be made to serve a double purpose.